1. Field
The present invention relates generally to wireless power, and more specifically to devices for wirelessly transmitting power to an electronic device and methods of operation thereof.
2. Background
Typically, each battery powered device requires its own charger and power source, which is usually an AC power outlet. This becomes unwieldy when many devices need charging.
Approaches are being developed that use over the air power transmission between a transmitter and the device to be charged. These generally fall into two categories. One is based on the coupling of plane wave radiation (also called far-field radiation) between a transmit antenna and receive antenna on the device to be charged which collects the radiated power and rectifies it for charging the battery. Antennas are generally of resonant length in order to improve the coupling efficiency. This approach suffers from the fact that the power coupling falls off quickly with distance between the antennas. So charging over reasonable distances (e.g., >1-2 m) becomes difficult. Additionally, unintentional radiation (e.g., due to plane wave radiation) can interfere with other systems if not properly controlled through filtering.
Other approaches are based on inductive coupling between a transmit antenna embedded, for example, in a “charging” mat or surface and a receive antenna plus rectifying circuit embedded in the host device to be charged. This approach has the disadvantage that the spacing between transmit and receive antennas must be very close (e.g. millimeters). Though this approach does have the capability to simultaneously charge multiple devices in the same area, this area is typically small, hence the user must locate the devices to a specific area.
As will be understood by a person having ordinary skill in the art, chargeable devices may require a steady level of power to be adequately charged. For example, to conform to high power USB specifications, a power source should supply a steady source of 5 volt power at 500 milliamps (2.5 watts) to a chargeable device to successfully begin, continue and accurately terminate a charge cycle upon a battery reaching a fully charged state. Conventionally, power adapters (e.g., AC or DC) have been used to provide this steady source of power. As will also be understood by a person having ordinary skill in the art, wireless chargers may not be configured to supply adequate power levels and, furthermore, may periodically interrupt power to a chargeable device to “power share” among more than one chargeable device. This may lead to a failure to initiate a charge, early termination of charge and/or inaccurate battery state-of-charge measurements. A need exists for devices, systems and methods for supplying a steady level of power to a chargeable electronic device for adequate charging thereof.